The Malthusian trap is the putative lack of sustainability of improvements in a society's standard of living because of population growth. It is named for Thomas Robert Malthus, who suggested that while technological advances could increase a society's supply of resources, such as food, and thereby improve the standard of living, the resource abundance would enable population growth, which would eventually bring the per capita supply of resources back to its original level. Some economists contend that since the industrial revolution, mankind has broken out of the trap. Others argue that the continuation of extreme poverty indicates that the Malthusian trap continues to operate. Others further argue that due to lack of food availability coupled with excessive pollution in developing countries show more evidence of the trap 
Malthus' theoretical argument
Malthus argued that society has a natural propensity to increase its population, a propensity that causes population growth to be the best measure of the happiness of a people: "The happiness of a country does not depend, absolutely, upon its poverty, or its riches, upon its youth, or its age, upon its being thinly, or fully inhabited, but upon the rapidity with which it is increasing, upon the degree in which the yearly increase of food approaches to the yearly increase of an unrestricted population."
However, the propensity for population increase also leads to a natural cycle of abundance and shortages:
We will suppose the means of subsistence in any country just equal to the easy support of its inhabitants. The constant effort towards population...increases the number of people before the means of subsistence are increased. The food therefore which before supported seven millions, must now be divided among seven millions and a half or eight millions. The poor consequently must live much worse, and many of them be reduced to severe distress. The number of labourers also being above the proportion of the work in the market, the price of labour must tend toward a decrease; while the price of provisions would at the same time tend to rise. The labourer therefore must work harder to earn the same as he did before. During this season of distress, the discouragements to marriage, and the difficulty of rearing a family are so great, that population is at a stand. In the mean time the cheapness of labour, the plenty of labourers, and the necessity of an increased industry amongst them, encourage cultivators to employ more labour upon their land; to turn up fresh soil, and to manure and improve more completely what is already in tillage; till ultimately the means of subsistence become in the same proportion to the population as at the period from which we set out. The situation of the labourer being then again tolerably comfortable, the restraints to population are in some degree loosened; and the same retrograde and progressive movements with respect to happiness are repeated.— Thomas Malthus, 1798. An Essay on the Principle of Population, Chapter II.
Evidence to support the theory
Research indicates that technological superiority and higher land productivity had significant positive effects on population density but insignificant effects on the standard of living during the time period 1–1500 AD. In addition, scholars have reported on the lack of a significant trend of wages in various places over the world for very long stretches of time. In Babylonia during the period 1800 to 1600 BC, for example, the daily wage for a common laborer was enough to buy about 15 pounds of wheat. In Classical Athens in about 328 BC, the corresponding wage could buy about 24 pounds of wheat. In England in 1800 AD the wage was about 13 pounds of wheat.:50 In spite of the technological developments across these societies, the daily wage hardly varied. In Britain between 1200 and 1800, only relatively minor fluctuations from the mean (less than a factor of two) in real wages occurred. Following depopulation by the Black Death and other epidemics, real income in Britain peaked around 1450-1500 and began declining until the British Agricultural Revolution.
Robert Fogel published a study of lifespans and nutrition from about a century before Malthus to the 19th century that examined European birth and death records, military and other records of height and weight that found significant stunted height and low body weight indicative of chronic hunger and malnutrition. He also found short lifespans that he attributed to chronic malnourishment which left people susceptible to disease. Lifespans, height and weight began to steadily increase in the UK and France after 1750. Fogel's findings are consistent with estimates of available food supply.
The rapid increase in the global population of the past century exemplifies Malthus's predicted population patterns, whereby expansion of food supply has encouraged population growth. "Neo-Malthusianism" may be used as a label for those who are concerned that overpopulation may increase resource depletion or environmental degradation to a degree that is not sustainable. Many in environmental movements express concern over the potential dangers of population growth. In 1968, ecologist Garrett Hardin published an influential essay in Science that drew heavily from Malthusian theory. His essay, "The Tragedy of the Commons," argued that "a finite world can support only a finite population" and that "freedom to breed will bring ruin to all." The Club of Rome published a famous book entitled The Limits to Growth in 1972. Paul R. Ehrlich is a prominent neo-Malthusians who first raised concerns in 1968 with the publication of The Population Bomb.
Theory that society has overcome the trap
The view that a "breakout" from the Malthusian trap has led to an era of sustained economic growth is explored by "unified growth theory". One branch of unified growth theory is devoted to the interaction between human evolution and economic development. Some argue that natural selection during the Malthusian epoch selected beneficial traits to the growth process and brought about the Industrial Revolution.
Some researchers contend that a British breakout occurred due to technological improvements and structural change away from agricultural production, while coal, capital, and trade played a minor role. Economic historian Gregory Clark has argued, in his book A Farewell to Alms, that a British breakout may have been caused by differences in reproduction rates among the rich and the poor (the rich were more likely to marry, tended to have more children, and, in a society where disease was rampant and childhood mortality at times approached 50%, upper-class children were more likely to survive to adulthood than poor children.) This in turn led to sustained "downward mobility": the descendants of the rich becoming more populous in British society and spreading middle-class values such as hard work and literacy.
- Galor, Oded (2005). "From Stagnation to Growth: Unified Growth Theory". Handbook of Economic Growth. 1. Elsevier. pp. 171–293.
- Clark, Gregory (2007). A Farewell to Alms: A Brief Economic History of the World. Princeton University Press. ISBN 978-0-691-12135-2.
- Julia Zinkina & Andrey Korotayev. Explosive Population Growth in Tropical Africa: Crucial Omission in Development Forecasts (Emerging Risks and Way Out). World Futures 70/2 (2014): 120–139.
- Tisdell, Clem (1 January 2015). "The Malthusian Trap and Development in Pre-Industrial Societies: A View Differing from the Standard One" (PDF). University of Queensland. Retrieved 26 February 2017.
- Malthus, Essay on the Principle of Population, Ch. VII.
- Engels, Fredrick (1892). The Condition of the Working-Class in England in 1844. London: Swan Sonnenschein & Co. Engels wrote that poverty and poor living conditions in 1844 had largely disappeared.
- Fogel, Robert W. (2004). The Escape from Hunger and Premature Death, 1700-2100. London: Cambridge University Press. ISBN 0521808782.
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- Allen, R. C. (2001). "The Great Divergence in European Wages and Prices from the Middle Ages to the First World War". Explorations in Economic History. 38 (4): 411–447. doi:10.1006/exeh.2001.0775.
- Overton, Mark (1996). Agricultural Revolution in England: The transformation of the agrarian economy 1500-1850. Cambridge University Press. ISBN 978-0-521-56859-3.
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- Pierre Desrochers; Christine Hoffbauer (2009). "The Post War Intellectual Roots of the Population Bomb" (PDF). The Electronic Journal of Sustainable Development. 1 (3). Archived from the original (PDF) on March 2, 2012. Retrieved 2010-02-01.[unreliable source?]
- Hardin, Garrett (1968). "The Tragedy of the Commons". Science. 162 (3859): 1243–1248.
- Wouter van Dieren, ed. (1995). Taking Nature Into Account: A Report to the Club of Rome. Springer Books. ISBN 978-0-387-94533-0.
- Korotayev, A.; et al. (2011). "A Trap At The Escape From The Trap? Demographic-Structural Factors of Political Instability in Modern Africa and West Asia". Cliodynamics. 2/2: 1–28.
- Galor, Oded; Moav, Omer (2002). "Natural Selection and The Origin of Economic Growth". Quarterly Journal of Economics. 117 (4): 1133–1191. doi:10.1162/003355302320935007.
- Tepper, Alexander and Karol J. Borowiecki. Accounting for Breakout in Britain: The Industrial Revolution through a Malthusian Lens (2013). Federal Reserve Bank of New York Staff Report 639. Available at: https://ideas.repec.org/p/fip/fednsr/639.html
- Malthus, Thomas Robert (1826). An Essay on the Principle of Population: A View of its Past and Present Effects on Human Happiness; with an Inquiry into Our Prospects Respecting the Future Removal or Mitigation of the Evils which It Occasions (Sixth ed.). London: John Murray. Retrieved 2008-11-22.
- Pomeranz, Kenneth (2000). The Great Divergence: China, Europe, and the Making of the Modern World Economy. ISBN 0-691-09010-6.
- Rosen, William (2010). The Most Powerful Idea in the World. New York: Random House. ISBN 978-1-4000-6705-3.